- Reflected by the leaf
- Of the wrong wavelength to be absorbed by chlorophyll
- Transmitted straight through the leaf
- Consumed due to the process of photosynthesis
- Lost by respiration
Primary Consumers:
Primary consumers are heterotropic; they obtain their nutrition by consuming other organisms. They obtain their energy by eating producers e.g. plants, however only a small proportion of the energy intake from feeding will be available as energy to a secondary consumer. Energy is lost from the system in:
- The process of respiration
- Urine
- Faeces
- Heat
- The production of biomass i.e. the energy available to a secondary consumer
Energy lost through respiration
At each trophic level, a portion of the energy obtained from nutrition is used for respiration. Organic compounds e.g. carbohydrates, are oxidised, causing the release of energy used to power metabolic reactions such as:
- Cell division
- Muscle contraction
- Synthesis of other compounds such as proteins and fats
- Active transport of ions
During these processes energy is lost as heat as the processes are not 100% efficient.
Other types of Producers
Photoautotrophs include plants, algae and cyanobacteria which convert the energy sunlight into carbon dioxide and water. Chemoautotrophs obtain all of their energy from chemical reactions, which they use to synthesize organic molecules. Nitrogen fixing bacteria, found in soil are chemoautotrophs. They convert ammonia into nitrites or nitrites into nitrates; which is an oxidation reaction, causing energy to be released. The bacteria use this energy to synthesize carbohydrates and simple organic molecules using carbon dioxide and water. Bacterium found near ocean beds and those near volcanic vents obtain energy through chemical reactions, as sunlight is unable to reach such depths. Primary consumers of these bacterium include marine worms.
Energy Flow through an Ecosystem
Eventually, all living matter dies and becomes detritus; the food,which detrivores (decomposers such as bacteria and fungi) consume. Although the energy flow on earth is an open system i.e. solar radiation enters the earth constantly, the flow of energy is not natural. Human influence has affected the energy flow in the ecosystem. Fossil fuels such as natural gas, oil and coal are extracted from the ground and when combusted, the release vast quantities of energy, and also energy lost as heat. This additional heat on earth is causing global warming making it possible in colder countries to grow crops they otherwise wouldn’t have been able to grow at lower temperatures. This unbalances the energy flow cycle as in some areas, more producers will grow and in others, certain species of consumers e.g. coral will die.
Trophic Levels and Food Chains
Trophic levels are steps in the food chain, which represent autotrophs and heterotrophs in the order that they are consumed. Due to the loss of energy by respiration, it is unusual to have more than 5 trophic levels in a food chain. A food chain is a sequence, which represents the way in which energy is transferred from one organisms to another in a community
Food Web
A Food Web is a diagram, which shows the way in which all the different species of organism in a community depend on each other for food. A food web is made up of many interconnected food chains. It is more accurate than a food chain, as it represents more complex eating habbits i.e. that consumers usually eat have a varied diet and eat more than one organism.
Ways of Presenting Energy Flow within an Ecosystem
The following graphical forms can be used:
Pyramids of numbers
It is a representation of the number of organisms at each trophic level at a given moment in time. The length or area of the rectangle represents the number of organisms in that particular trophic level. Usually, the size of each organism increases, ascending the pyramid
Pyramids of Biomass
It represents the biomass (number of individuals x mass of each individual) at each trophic level at a specific moment in time. It should prevent inversion problems, which may occur in pyramids of number.
Pyramids of Energy
It represents the flow of energy through each trophic level of an ecosystem during a fixed time period (usually one year to account for seasonal effects .) It compares productivity over time, hence no inversions occur.
Conclusion
Energy flowing through an ecosystem usually originates from the sun, which is transferred to primary consumers by photoautotrophs. Alternatively, chemoautotrophs, such as bacteria found near ocean beds, synthesize energy from chemical reactions and pass on this energy to consumers such as marine worms.
Energy is used to assimilate organic compounds and is lost through heat and respiration. Only about 10% of the energy ingested by a consumer is passed on to the next trophic level, as systems e.g. the human system is not 100% efficient.
Energy loss through an ecosystem can be observed ascending pyramids of number, biomass and energy.